Magnetic memory device

ABSTRACT

A memory device is proposed which enables to guarantee the operation of MRAM elements being magnetically shielded against a large external magnetic fields without being affected by an internal leakage magnetic field. The MRAM elements  30  which are shielded by magnetic shield layers  33, 34  are placed at an intermediate region  41  avoiding an edge region  43  and a center region  42  of the magnetic shield layers  33, 34  so that the MRAM element is secured to operate normally without being affected by the internal leakage magnetic field avoiding the edge region  43  where the magnetic shield effect is reduced by the exterior magnetic field, and avoiding the central region  42  where the internal leakage magnetic field is large

TECHNICAL FIELD

The present invention relates to a magnetic memory device constructed asa magnetic random access memory (MRAM) or a so-called non-volatile MRAM(Magnetic Random Access Memory) which is comprised of memory elementsmade by laminating a magnetization pinned layer in which the orientationof magnetization is fixed and a magnetic layer in which the orientationof magnetization is changeable, or to any magnetic memory devicecomprising memory elements having a magnetic layer capable of beingmagnetized.

BACKGROUND ART

With a rapid prevalence of information communication equipment, inparticular, of personal compact equipment such as portable terminals, afurther improvement in performance inclusive of larger scaleintegration, faster speed, lower power consumption or the like isdemanded for their elements such as memories, logics and the like.

In particular, the non-volatile memory is considered to be indispensablein the age of ubiquitous. If a power supply is exhausted or a powertrouble occurs, or even if a connection between the server and thenetwork is cut off by any failure, the non-volatile memory can protectimportant information including personal information. Further, althoughrecent portable equipment is designed to hold unnecessary circuitryblocks in a standby state in order to suppress power consumption as muchas possible, if a non-volatile memory that can function both as a highspeed work memory and as a large capacity storage memory is realized,losses of the power consumption and the memory can be eliminated. Stillfurther, if a high speed and large capacity non-volatile memory can berealized, an “instant-on” function that can be instantaneously activatedupon power-on operation becomes possible.

As the non-volatile memories, there are also cited a flash memory whichuses semiconductors, a FRAM (Ferroelectric Random Access Memory) whichuses a ferroelectric material, and the like.

However, the flash memory has a drawback that a write speed is low inthe order of _(″) seconds. On the other hand, also in the FRAM, problemsare cited that because the number of rewritable frequencies is 10¹² to10¹⁴, the endurance thereof is too small to completely replace SRAM(Static Random Access Memory) or DRAM (Dynamic Random Access Memory),and that micro fabrication of a ferroelectric capacitor is not easy.

Drawing attention as a non-volatile memory having no such drawbacks asdescribed above, featuring a high speed, large capacity (large scaleintegration) and a low power consumption, is a so-called MRAM (MagneticRandom Access Memory), for example, described by Wang et al., in IEEETrans. Magn. 33 (1997), 4498, which has begun to draw much attention byrecent remarkable improvements in the characteristics of TMR (TunnelMagnetoresistance) materials.

An MRAM is a semiconductor memory which utilizes a magnetoresistanceeffect based on a spin dependent conducting phenomenon characteristic toa nano-magnetic substance, and is a non-volatile memory capable ofretaining information without power supply from external.

Moreover, because of its simple structure, MRAM is easy to integrateinto a large scale IC, and because of its recording of information basedon spinning of magnetic moments, the number of rewritable frequencies islarge, and also its access time is expected to become very fast asreported by R. Scheuerlein et al., in the ISSCC Digest of TechnicalPapers, pp. 128-129, February 2000, where operability at 100 MHz wasalready reported.

Such a MRAM will be described more in detail. As illustrated in FIG. 14,a TMR element 10 which constitutes a memory element in a memory cell ofMRAM includes a memory layer 2 in which magnetization is relativelyeasily rotated, and magnetization pinned layers 4, 6, laminated on asupport substrate 9.

The magnetization pinned layer has two magnetization pinned layers of afirst magnetization pinned layer 4 and a second magnetization pinnedlayer 6, and a conductive layer 5 is interposed therebetween forantiferromagnetically coupling these magnetic layers. As a memory layer2 and magnetization pinned layers 4 and 6, a ferromagnetic material madeof nickel, iron or cobalt, or an alloy thereof is used. Also, as amaterial of the conductive layer 5, any of ruthenium, copper, chrome,gold, silver or the like can be used. The second magnetization pinnedlayer 6 abuts an antiferromagnetic material layer 7. An exchangeinteraction occurring between these layers causes the secondmagnetization pinned layer 6 to have a strong unidirectional magneticanisotropy. As a material of the antiferromagnetic material layer 7, amanganese alloys with such as iron, nickel, platinum, iridium, rhodium,or cobalt or nickel oxides may be used.

Further, between the memory layer 2 as the magnetic layer and the firstmagnetization pinned layer 4 there is sandwiched a tunnel barrier layer3 which is an insulating body made of an oxide or nitride of aluminum,magnesium, silicon and the like, and functions to cut off a magneticcoupling between the memory layer 2 and the magnetization pinned layer 4and also to pass a tunneling current therethrough. These magnetic layersand conductive layers are formed basically by a sputtering method,however, the tunnel barrier layer 3 can be obtained by oxidizing ornitriding a metal film deposited by sputtering. A top coat layer 1,which has a function to prevent mutual diffusion between the TMR element10 and wiring to be connected thereto, to reduce a contact resistance,and to inhibit oxidization of the memory layer 2, can be made using sucha material as Cu, Ta, TiN or the like. An underlayer electrode 8 is forconnection with a switching element to be connected in series with theTMR element. This underlayer electrode 8 may serve also as anantiferromagnetic material layer 7.

In the memory cell constructed as described above, although informationis read out by detecting changes in a tunneling current by themagnetoresistance effect to be described later, the effect thereofdepends on relative orientations of magnetization in the memory layerand the magnetization pinned layer.

FIG. 15 is an enlarged perspective view showing a simplified portion ofa general MRAM. Here, although a read-out circuit portion is omitted forsimplification, there are included, for example, 9 pieces of memorycells, and mutually intersecting bit lines 11 and writing word lines 12.At each intersection therebetween, a TMR element 10 is disposed. Writingto the TRM element 10 is carried out in such a manner that by passing acurrent through the bit line 11 and the write word line 12, and by usinga synthetic magnetic field resulting from respective magnetic fieldsgenerated therefrom, an orientation of magnetization in the memory layer2 in the TMR element 10 disposed at each intersection of the bit line 11and the write word line 12 is caused to rotate parallel or anti-parallelrelative to that in the magnetization pinned layer.

FIG. 16 schematically illustrates a cross section of a memory cell, inwhich, for example, an n-type field effect transistor 19 for read out isdisposed, comprising a gate insulation film 15, a gate electrode 16, asource region 17 and a drain region 18 which are formed in a p-type wellregion 14 formed in a p-type silicon semiconductor substrate 13, andabove thereof there are disposed a write word line 12, a TMR element 10and a bit line 11. To the source region 17, a sense line 21 is connectedvia a source electrode 20. The field effect type transistor 19 functionsas a switching element for read-out, and a wiring 22 for reading whichis wired out from between the word line 12 and the TMR element 10 isconnected to the drain region 18 via a drain electrode 23. By way ofexample, the transistor 19 may be of any of n-type or p-type fieldeffect transistors, and is not limited thereto, and various types ofother switching elements such as diodes, bipolar transistors, MESFET(Metal Semiconductor Field Effect Transistors) and the like can be used.

FIG. 17 shows an equivalent circuit of an MRAM, which has, for example,6 pieces of memory cells, mutually intersecting bit lines 11 and writeword lines 12, and TMR elements 10 provided at each intersection ofthese write word lines together with a field effect transistor 19 forselection of an element for reading which is connected to the TMRelement 10 and to a sense line 21. The sense line 21 which is connectedto a sense amplifier 27 detects stored information. By way of example,numeral 24 in the drawing depicts a bidirectional write word linecurrent drive circuit, and 25 depicts a bit line current drive circuit.

FIG. 18 is an asteroid curve showing write conditions to write to theMRAM, and indicates a threshold value for reversing the orientation ofmagnetization in the memory layer by a magnetic field H_(EA) applied inthe directions of the easy axis of magnetization and a magnetic fieldH_(HA) applied in the directions of the difficult axis of magnetization.If a synthetic magnetic field vector is produced outside this asteroidcurve, a reversal of the magnetic field occurs, however a syntheticmagnetic field produced inside the asteroid curve does not cause thecell to be reversed from either one of its current bistable state to theother. Further, also in any cells other than at intersections of theword lines and the bit lines both passing through the currents, becausea singular magnetic field generated either by the word line or the bitline is applied thereto, if a magnitude thereof exceeds amonodirectional reversal magnetic field Hk, the orientation ofmagnetization in any cells outside the aforementioned intersections maybe reversed. Therefore, it is arranged to permit a selective writing toa selected cell only when the synthetic magnetic field falls in agrey-colored region in the drawing.

As described above, as to the MRAM, it is general that by use of twowrite lines of the bit line and the word line, and utilizing theasteroid magnetization reversal characteristics, only a designated cellis allowed selectively to write in to be effected by reversal of amagnetic spin. A synthetic magnetic field in a unit memory region isdetermined by a vector synthesis of a magnetic field applied in thedirection of the easy axis of magnetization H_(EA) and a magnetic fieldapplied in the direction of the difficult axis of magnetization H_(HA).A current passing through the bit line applies a magnetic field in thedirection of the easy axis of magnetization H_(EA) to the cell, and acurrent passing through the word line applies a magnetic field in thedirection of the difficult axis of magnetization H_(HA) to the cell.

FIG. 19 illustrates operation of reading from MRAM. Here, a schematicdiagram of a layer structure of a TMR element 10 is shown, in which theaforementioned magnetization pinned layer is depicted as a monolayer 26,and parts other than a memory layer 2 and a tunnel barrier layer 3 areomitted for simplification.

That is, as described above, writing of information is carried out bycausing a synthetic magnetic field produced at the intersection betweenthe bit lines 11 and the word lines 12 wired in a mesh to reverse themagnetic spin in the cell so as to store the information as “1” or “0”.Further, reading of information is carried out by utilizing a TMR effectwhich makes use of the magnetoresistance effect. Here, the TMR effectrefers to such a phenomenon that a value of electrical resistance ischanged depending on the orientation of the magnetic spin, and that bydetecting a high resistance state if the magnetic spin is orientedanti-parallel (reverse direction) and a low resistance state if themagnetic spin is oriented parallel (same direction), information of “1”and “0” is detected. This reading is carried out by causing a readcurrent (tunneling current) to pass through between the word line 12 andthe bit line 11, and reading out an output therefrom in accordance withthe aforementioned high resistance or low resistance to the sense line21 via the field effect transistor 19 for reading.

As described above, although the MRAM is expected as a high speed andlarge capacity non-volatile memory, because of use of the magneticmaterial for retention of information, there is such a problem thatinformation is erased or rewritten by the effect of an external magneticfield. This is because that a reversing magnetic field H_(SW) in thedirections of the easy axis of magnetization and the difficult axis ofmagnetization described with reference to FIG. 18 is small in a range of20 to 200 Oe, though it depends on a material, and a few mA in terms ofan electric current (R. H. Koch et al., Phys. Rev. Lett. 84, 5419(2000), J. Z. Sun et al., 2001 8^(th) Joint Magnetism and MagneticMaterial). In addition, because a coercive force (Hc) when writing is ina range of approximately a few Oe to 10 Oe, if an internal leakagemagnetic field greater than that resulting from an external magneticfield is applied, it sometimes becomes impossible selectively to writeto a designated memory cell.

Therefore, as one step to actual application of the MRAM, it is ardentlydesired to establish countermeasures against external magnetic fields,that is, an effective magnetic shield structure for shielding theelements from external electromagnetic waves.

An environment in which an MRAM is packaged and used is mainly on a highdensity packaging substrate, and inside electronics equipment. Althoughit depends on the types of electronic equipment, by recent developmentsof high density packaging techniques, there are densely packaged avariety of semiconductor elements, communication elements, a micro-motorand the like on a high density packaging substrate, and also antennaelements, various mechanical parts, power source and the like aredensely packaged inside the electronic equipment thereby constructing aunit of equipment.

A capability of a mixed or hybrid packaging as described above is one ofthe features of an MRAM as anon-volatile memory, however, because of itsenvironment surrounding the MRAM in which various magnetic fieldcomponents in a broad frequency range including dc, low frequencies tohigh frequencies are mixed and coexist, it is required, in order toensure reliability of information retaining in MRAM, to improve thedurability thereof against the external magnetic fields by developing anew packaging method and a new shield structure of the MRAM itself.

As to a magnitude of such external magnetic fields, for example, in amagnetic card such as a credit card or a bank cash card, it is specifiedto have durability against a magnetic field from 500 to 600 Oe.Therefore, in the field of the magnetic card, a magnetic material havinga large coercive force such as a Co clad gamma-Fe₂O₃, Ba ferrite or thelike are used in compliance therewith. Also, in the field of prepaidcards, it is necessary to have durability against magnetic fields from350 to 600 Oe. Because the MRAM element is packaged inside electronicequipment, and is a device expected to be carried on, it needs to haveenough durability against strong external magnetic fields equivalent tothat of the magnetic cards, and in particular, because of the reasondescribed above, a magnitude of an internal (leakage) magnetic field isrequired to be suppressed below 20 Oe, or preferably below 10 Oe.

As a magnetic shield structure of MRAM, it is proposed to use aninsulating ferrite (MnZn ferrite and NiZn ferrite) layer as apassivation film of an MRAM element so as to provide a magneticshielding characteristic (refer to U.S. Pat. No. 5,902,690,specification (column 5) and drawings (FIG. 1 & FIG. 3)). It is alsoproposed to attach a high permeability magnetic body such as Permalloyon the top and bottom of the package so as to provide a magneticshielding effect and prevent penetration of a magnetic flux into theinternal element (refer to U.S. Pat. No. 5,939,772, specification column2, FIGS. 1, 2). Further, a structure of a shield lid made of a magneticmaterial such as soft iron or the like for cladding the element isdisclosed (refer to Japanese Patent Application Publication No.2001-250206, right-hand column on page 5, FIG. 6).

In order to prevent penetration of an external magnetic flux into thememory cell of MRAM, it is most important to clad the element with amagnetic material having a high permeability so as to provide a magneticpath thereby allowing no magnetic flux to penetrate any further.

However, when the passivation film of the element is formed from ferriteas disclosed in U.S. Pat. No. 5,902,690, because of a low magneticsaturation in the ferrite itself (for example, 0.2 to 0.5 tesla (T) ingeneral ferrite materials), it is impossible completely to preventpenetration of external magnetic fields. Magnetic saturation in theferrite itself is approximately 0.2 to 0.35 T in NiZn ferrite, and 0.35to 0.47 T in MnZn ferrite, however, a magnitude of an external magneticfield penetrating into the MRAM element is as large as several hundredsOe, thereby only with such a degree of saturation magnetization providedby the ferrite, a permeability becomes almost “1” due to magneticsaturation in the ferrite thereby disabling its function. Further,although a film thickness is not described in U.S. Pat. No. 5,902,690,because a thickness of a normal passivation film is about 0.1 _(″)m orso at most, it is too thin to serve as a magnetic shield layer, therebyany substantial effect cannot be expected. Moreover, in the case ifferrite is to be used as the passivation film, because the ferrite is anoxide magnetic material, when it is deposited by sputtering, an oxygendefect tends to occur, thereby making it difficult to obtain a perfectferrite to be used as the passivation film.

Further, in U.S. Pat. No. 5,939,772, a structure for sandwiching thepackage between the upper and the bottom Permalloy layers is disclosed.By use of the Permalloy, a higher shield performance than that of theferrite passivation film is obtained. However, although the permeabilityof the Mu metal disclosed in U.S. Pat. No. 5,939,772 is very high tobecome _(″)i=100,000 or so, the magnetic saturation thereof is very lowto be 0.7 to 0.8 T, at which it will easily saturate to an externalmagnetic field consequently to become _(″)=1, therefore, there is aproblem that in order to obtain a perfect magnetic shielding effect, athickness of the shield layer must be increased considerably large.Therefore, as the structure for enabling to prevent penetration ofmagnetic fields of several hundreds Oe, in practice, it is not yetperfect as the magnetic shield layer in view of both drawbacks that thesaturation magnetization thereof is too small and that the thicknessthereof is too thin.

Still further, in Japanese Patent Application Publication No.2001-250206, although a magnetic shield structure using soft iron or thelike is disclosed, as this covers only the upper portion of the element,it is not perfect as the magnetic shield. Also, the magneticcharacteristics thereof are not sufficient because that the saturationmagnetization of the soft iron is 1.7 T and the permeability thereof is_(″)i=300 or so. Therefore, even if a magnetic shield is fabricatedusing the structure disclosed in Japanese Patent Application PublicationJP-A Laid-Open No. 2001-250206, it would be very difficult to completelyprevent the penetration of external magnetic fields.

The present invention is contemplated to solve the aforementionedproblems associated with the prior art, and to provide means formagnetically shielding MRAM elements sufficiently against large externalmagnetic fields, and also to guarantee reliable operation of the MRAMelements in an environment surrounding the MRAM elements which producesvarious magnetic fields.

DISCLOSURE OF THE INVENTION

The present invention relates to a magnetic memory device comprisingmemory elements each having a magnetic layer capable of magnetization,and in particular, to a magnetic memory device (hereinafter referred toas a magnetic memory device according to the embodiment of the presentinvention) which is constructed as a magnetic random access memory(MRAM) which has memory elements each comprising by laminating amagnetization pinned layer in which the orientation of magnetization ispinned (fixed) and a magnetic layer in which the orientation ofmagnetization is changeable, and further comprising a magnetic shieldlayer for magnetically shielding each of the memory elements, whereinthe aforementioned memory elements are characterized by being disposedavoiding an edge portion and a center portion of the aforementionedmagnetic shield layer.

As a result of diligent studies and discussions on the aforementionedproblems, the inventors of the present invention have discovered thatthe magnetic shield effect attenuates with a progress of the magneticsaturation in a magnetic material of the magnetic shield layer, that thesaturation of magnetization in a magnetic material, for example, in theshape of a plate, starts from a location where demagnetization becomesminimal (that is, the farthest point from the edge portion), and that inthe case where a magnetic shield layer is applied to the package, theweakest portion of the magnetic shield effect is a central portion ofthe package.

On the basis of such recognition described above, the inventors of thepresent invention have discovered that by placing the memory elementsavoiding the edge portion and the center portion of the magnetic shieldlayer, that is, by placing the memory elements in a region between thecenter portion of the magnetic shield layer, in which magneticsaturation easily tends to occur thereby allowing for an internalleakage magnetic field strength to become large, and the edge portion ofthe magnetic shield layer, in which no magnetic shield effect existsbecause of a direct exposure to an external magnetic field, the memoryelements are ensured to operate normally without being affected by theinternal leakage magnetic field, thereby enabling successfully toachieve the magnetic memory device according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 2B is a cross-sectional view of a schematic diagram of anMRAM package according to a preferred embodiment of the presentinvention (FIG. 1A), and a plan view thereof more in specific (FIG. 1B).

FIG. 2 is a cross-sectional view of a schematic diagram of another MRAMpackage according to the preferred embodiment of the present invention.

FIG. 3 is a cross-sectional view in schematic of still another MRAMpackage according to the preferred embodiment of the present invention.

FIGS. 4A to 4B are cross-sectional views in schema of MRAM packagesaccording to still more another preferred embodiment of the presentinvention.

FIG. 5 is a cross-sectional view of a schematic diagram of a measuringapparatus for measuring an internal magnetic field strength at aposition between magnetic shield layers according to the embodiment ofthe present invention.

FIG. 6 is a distribution diagram of internal magnetic field strengths inthe case where a high permeability material of Fe-75Ni-5Mo-1Cu was used,and when an external magnetic filed of 500 Oe was applied, according tothe embodiment of the present invention.

FIG. 7 is a distribution diagram of internal magnetic field strengths inthe case where a high permeability material of Fe-49Co-2V was used, anda thickness of a magnetic shield layer (shield foil) was at200_(″m, and when an external magnetic field of) 500 Oe was applied,according to the embodiment of the present invention.

FIG. 8 is a table showing internal magnetic field strengths versusthicknesses of magnetic shield layers when Fe-49Co-2V was used and anexternal magnetic field of 500 Oe was applied likewise.

FIG. 9 is a distribution diagram showing internal magnetic fieldstrengths versus lengths of magnetic shield layers with the thicknessthereof changed variously, when said layers were made of Fe-49Co-2V andan external magnetic field of 500 Oe was applied likewise.

FIG. 10 is a table showing internal magnetic field strengths versuslengths of the magnetic shield layer which uses Fe-49 Cc-2V underapplication of an external magnetic field at 500 Oe.

FIG. 11 is a distribution diagram of internal magnetic field strengthversus lengths of magnetic shield layers having specified variouslengths, made of Fe-49Co-2V, under application of an external magneticfield at 500 Oe, according to the embodiment of the invention.

FIG. 12 is a distribution diagram of internal magnetic field strengthsversus lengths of magnetic shield layers relative to a standardizedlength thereof according to the embodiment of the invention.

FIGS. 13A to 13B is a plan view showing an area within a package inwhich MRAM elements can be disposed (FIG. 13A) and a plan view showing astate of arrangements thereof (FIG. 13B) according to the embodiment ofthe invention.

FIG. 14 is a perspective view in schema of a TMR element in MRAM.

FIG. 15 is a perspective view in schema of a portion of a memory cellunit in MRAM.

FIG. 16 is a cross-sectional view of a schematic diagram of a memorycell in MRAM.

FIG. 17 is an equivalent circuit of an MRAM.

FIG. 18 is a diagram showing magnetic field response characteristicswhen writing to MRAM.

FIG. 19 is a diagram showing a principle of operation when reading fromMRAM.

BEST MODE FOR CARRYING OUT THE INVENTION

In a magnetic memory according to the preferred embodiment of theinvention, when a length from one side of a magnetic shield layer to anopposed side thereof is assumed to be L, it is desirable for memoryelements to be disposed in a region between a position at 0.1 L inwardfrom the above-mentioned one side and a position at 0.15 L outward fromthe center of the magnetic shield layer toward the above-mentioned oneside thereof, in consideration that an adverse effect by an internalleakage magnetic field can be easily avoided by the arrangementdescribed above.

In this case, assuming that the magnetic shield layer is provided onboth sides (top and bottom) of the memory element respectively, and thata distance between these magnetic shield layers, a length from theaforementioned one side of the magnetic shield layer to the opposed sidethereof, and an external magnetic field to be applied are constantrespectively, it is desirable for the aforementioned memory elements tobe disposed in a region between a position at 0.2 L inward from theaforementioned one side and a position at 0.15 L outward from the centerof the shield layer toward the aforementioned one side thereof.

Further, assuming that a distance between the aforementioned magneticshield layers, a thickness of the magnetic shield layers and an externalmagnetic field to be applied are constant respectively, it is desirablefor the aforementioned memory elements to be disposed in a regionbetween a position at 0.1 L inward from the aforementioned one sidethereof and a position at 0.2 L outward from the center of the shieldlayer toward the aforementioned one side thereof.

Then, in order for the magnetic shield layer to be able to exhibit themagnetic shield effect thereof, it is desirable for the magnetic shieldlayer to be disposed on the top and/or bottom of the package comprisingby sealing the memory elements therein, or/and on the upper portionand/or the lower portion of the memory elements within the package, andfurther preferably the memory elements are to be present almost alloverthe package.

Further, the magnetic shield layer, other than provided in the form of aflat film or plate, may have concave and/or convex portions on its filmor plate, or through-holes such as mesh or slits, in order to be able tomore effectively suppress the magnetic saturation.

Then, it is desirable for the magnetic shield layer to be formed of softmagnetic material that exhibits saturation magnetism at 1.8 tesla ormore in order to be able to lower the saturation magnetization in themagnetic shield layer.

The present invention is suitable to MRAM, however, this MRAM ispreferably constructed such that an insulating material layer or aconductive material layer is sandwiched between the aforementionedmagnetization pinned layer and the aforementioned magnetic layer, thatwith a magnetic field induced by passing a respective current throughwirings of a bit line and a word line provided on the top and the bottomof the memory element, the orientation of magnetization in theaforementioned magnetic layer is aligned in a prescribed directionthereby writing information thereto, and that this written informationis read out by use of the tunnel magnetoresistance effect (TMR effect)between the aforementioned wirings.

Now, by referring to the accompanying drawings, preferred embodiments ofthe present invention will be described more specifically in thefollowing.

FIG. 1A to FIG. 3 illustrate respective MRAM packages having varioustypes of magnetic shield structures according to the preferredembodiments of the present invention (FIG. 1A shows a cross-sectionalview in schematic cut out along line A-A′ in FIG. 1B which shows a planview of a package more specifically).

In these examples, MRAM elements (each being a chip including a memorycell portion and a peripheral circuitry portion) 30 as shown in FIGS. 14to 16 are mounted on a die pad 40 avoiding the edge portion and thecentral portion of the magnetic shield layers 33 and 34, then, allportions except for an external lead 31 (the die pad and the leadsection inclusive of their wiring are simply drawn) to be connected to apackage substrate (not shown) are sealed with a sealing material 32 suchas mold resin (e.g. epoxy resin). Here, the description of the MRAMelement 30 is omitted because of its similar structure and operationprinciple to those of the MRAM described already.

Further, according to the preferred embodiments of the presentinvention, there are shown an exemplary case (FIGS. 1A and 2B) wheremagnetic shield layers 33, 34 having a saturation magnetization at 1.8 Tor more are disposed on the top and the bottom surfaces of a sealingmaterial 32 which encapsulates MRAM elements 30 having built-in TMRelements together with other elements such as DRAM or the like (DRAM 45,DSP 46 and RF 47 to be described later), another exemplary case (FIG. 2)where the magnetic shield layers 33, 34 are disposed, within the sealingmaterial 32, on the upper portion of the MRAM element 30 and on thelower portion of the die pad 40, and still another exemplary case (FIG.3) where they are embedded in a non-contacting state, respectively.

Before sealing with the sealing material 32, it may be arranged suchthat in an intermediate region 41 of the magnetic shield layer 33, 34 byavoiding a central region 42 of the magnetic shield layer 33, 34 where amagnetic shield effect attenuates with saturation of magnetization, andwhere demagnetization becomes minimum due to a faster magneticsaturation therein, and also by avoiding an edge region 43 of themagnetic shield layer 33, 34 where the magnetic shield effect thereofbecomes smallest as exposed directly to an external magnetic field, theMRAM elements 30 are secured on the die pad 40 in advance, then, aftersealing thereof, the magnetic shield layers 33 and 34 are bonded to thetop and the bottom of the sealing material 32. Alternatively, it may bearranged such that by disposing the MRAM elements 30 in theaforementioned intermediate region 41 before sealing thereof, and bydisposing the magnetic shield layers 33, 34 at positions on both sidesof the die pad 40 in a die, then, they are sealed simultaneously.

In any cases of the above, the MRAM element 30 has a structure assandwiched between the magnetic shield layers 33, 34, and the magneticshield layers 33, 34 are formed integral with the package of the MRAM.As described above, that the magnetic shield layers 33, 34 constitute asandwich structure placed on the top and bottom of the MRAM (or on thetop and bottom of a MRAM hybrid semiconductor package), and that theycan be formed integral with the MRAM package provide for a mostdesirable structure for mounting on a circuit substrate.

In any of the magnetic shield structures illustrated in FIG. 1A to FIG.3, generally, the MRAM element 30 can be magnetically shielded from anexternal magnetic field to some degrees, however, with a saturation ofmagnetization in the magnetic material, occurrence of attenuation of themagnetic shield effect cannot be avoided, and in particular, in thecenter portion thereof demagnetization becomes minimum, and in the edgeportion of the magnetic shield layer 33, 34 where it is directlyaffected by the external magnetic field, the magnetic shield effectbecomes minimal. In these cases, although it is preferable for themagnetic shield layer 33, 34 to exist both on the top and the bottom ofthe MRAM element 30, it may exist only, at least, on one side thereof(in particular, on the top side of MRAM element).

However, according to the preferred embodiment of the present invention,the MRAM elements 30 are placed avoiding the edge portion and the centerportion of the magnetic shield layer 33, 34 so that the MRAM elements 30are ensured to operate normally without being affected by an internalleakage magnetic field. Moreover, because the intermediate region 41therebetween avoiding the center region 42 and the edge region 43 is aregion in which the MRAM elements 30 are essentially free from theinfluence of the internal leakage magnetic field, a thickness of themagnetic shield layer can be designed to become thinner, as a result,enabling to make the MRAM device compacter and light-weighted (whichwill be described later).

The magnetic shield layers 33, 34 illustrated in FIG. 1A to FIG. 3 arecomprised of a flat film, foil, or a plate, however, it is not limitedthereto, and it may be formed to have various shapes provided with, forexample, irregularities 35 as depicted in FIG. 4A, or through-holes 36in a mesh, slit or the like as depicted in FIG. 4B. The magnetic shieldlayers with the shape of FIG. 4A or 4 b, because of presence of a shapeanisotropy thereof not only in a circumferential edge portion thereofbut also in the portions of the irregularities or the through-holesthereof, demagnetization against an externally applied magnetic field isgenerated, thereby suppressing the magnetic saturation to provide ashield effect of improved characteristics.

In any of the magnetic shield structures depicted in FIGS. 1A to 4B,saturation magnetization of the magnetic shield layers 33, 34 is 1.8 Tor greater, which is substantially greater than those of a conventionalferrite, Permalloy or the like, and by disposing them on the sealingmaterial or in a predetermined position within the sealing material, anexcellent shield performance capable of suppressing the internal leakagemagnetic field strength can be obtained.

The inventors of the present invention carried out experiments in orderto achieve an appropriate environment that can guarantee a normaloperation of a unit of MRAM elements even if a large dc externalmagnetic field as large as 500 Oe at maximum is applied.

With a progress of high density packaging technologies, the MRAM isused, in practice, in a multiple pin hybrid type packaging as mounted inmixture with other functional elements. As these packaging structures,there are cited a QFP (Quad Flat Package), LQFP (Low Profile Quad FlatPackage), BGA (Ball Grid Array Package), LFBGA (Low Profile Fine PitchBall Grid Array Package), LFLGA (Low Profile Fine Pitch Land Grid ArrayPackage) and the like.

Taking into consideration these package structures, the presentinventors have studied a thinnest and most effective magnetic shieldmaterial. FIG. 5 shows a schematic diagram of an arrangement adopted inthe experiments for studying magnetic shield effects of these materials.As a model case, magnetic shield layers 33, 34 are mounted on the topand the bottom of a 160 pin QFP type package as shown in FIGS. 1A and1B, in which two sheets of shield layers of L: 28 mm×L: 28 mm aredisposed at a distance of D: 3.45 mm, then in the center therebetween agauss meter 37 is placed. Then, by applying a dc external magnetic fieldof 500 Oe parallel to the magnetic shield layers, and by moving thegauss meter 37 parallel to the magnetic shield layers, internal magneticfield strengths (leakage magnetic field strengths from the magneticshield layers) are measured from the edge portion to the center portionthereof.

An internal magnetic field strength distribution is shown in FIG. 6 forthe case where, as a typical material among various shield materials, asuper Permalloy: Fe-75Ni-5Mo-1Cu which is the highest permeabilitymaterial was used as the magnetic shield layer material in theexperiments. The Fe-75Ni-5Mo-1Cu has an initial permeability_(″)i=100000, and saturation magnetization Ms=0.8 T. The internalmagnetic field strengths are shown as a distribution over a length ofthe shield layer, that is, a length of 28 mm from one end to the otherend. The external magnetic field to be applied was set at 500 Oe, and athickness of the shield layer at 200_(″)m.

It is known from FIG. 6 that when a strong magnetic field of 500 Oe isapplied from external, the magnetic shield layer made of Fe-75Ni-5Mo-1Cusuffers a magnetic saturation, thereby allowing penetration ofmagnetization of 428 Oe in the center portion of the package and therebyeliminating the shield effect almost all. Therefore, even if thestructure to dispose the Mu metal layer as disclosed in U.S. Pat. No.5,939,772 is adopted, the shield effect thereof is difficult to expectin practice.

On the other hand, a distribution of internal magnetic field strengthsobtained using the experimental equipment of FIG. 5 is shown in FIG. 7,in which, in order to avoid magnetic saturation, a Permendur alloy:Fe-49Co-2V which is a high saturation magnetization material was used asthe magnetic shield layer material. The Fe-49Co-2V has an initialpermeability _(″)i=1200, and saturation magnetization Ms=2.3 T.

It is known from FIG. 7 that in the case where the Fe-49Co-2V was usedas the magnetic shield layer material, a magnetization strength thereofin the center portion of the package became 282 Oe, thereby enabling tosuppress the internal penetration magnetic field approximately to a halfcompared to that in the case where Fe-75Ni-5Mo-1Cu was used as itsmaterial. However, in an environment of 282 Oe, it is still difficultfor the MRAM to operate normally.

Thereby, using Fe-49Co-2V as the magnetic shield material, with a gapbetween the shield layers set constant, and a thickness of the shieldlayer changed variously, a magnetic field strength in the center portionof the sandwich structure thereof was measured, a result of which isshown in FIG. 8.

Namely, FIG. 8 indicates experiments carried out using the experimentalequipment shown in FIG. 5, in which a distance D between the magneticshield layers was set constant (3.45 mm), an external magnetic field tobe applied was set 500 Oe, and the thickness of the shield layers waschanged variously at 200, 250, 270, 300, 320, 350, 400, 600 and 800_(″)mrespectively, wherein the magnetic field strengths in the center portionbecame 282, 219, 193, 150, 117, 59, 18, 10, 10 Oe, respectively. As aresult, it is known that with an increase in the thickness of the shieldlayers, a magnitude of a penetrating magnetic field can be reduced.

From the result indicated in FIG. 8, in order to ensure for the MRAM tooperate normally, it is preferable to suppress the internal magneticfield strength as much as possible. Then, if an upper limit of theinternal magnetic field strength is set at 20 Oe, it is consideredconsequently that a high saturation magnetization material such asFe-49Co-2V or the like is to be used as a magnetic shield layer materialand a thickness of the shield layer is to be set 400_(″)m or more.However, in the age in demand of more compact and light-weightedelectronics devices, it is anticipated to become more difficult to mounttwo sheets of such a shield layer of 400_(″)m thick on the top andbottom within an electronic device. Nevertheless, if a stricter upperlimit to the internal magnetic field strength is set, it becomesnecessary for the thickness of the shield layers to be increasedfurther.

Thereby, a novel arrangement enabling for the MRAM to be avoided fromthe external leakage magnetic even with a thinner shield layer byadjustment of the position of MRAM to be disposed within the packagewill be described in the following.

FIG. 9 shows a result of measurements of internal magnetic fieldstrength distributions per various thicknesses of Fe-49Co-2V used as thematerial. The internal magnetic field strength shows a distributionrelative to a length of the shield layer, that is, within L: 28 mm ofFIG. 5. A gap between the shield layers was assumed constant (at 3.45mm), an external magnetic field to be applied was assumed 500 Oe, andthe thickness of the shield layer was varied 250, 270, 300, 320, 350,400 and 600_(″)m.

As a result, as shown in FIG. 9., it is known that although apenetrating magnetic field strength became larger in the center portionand the edge portion of the package, a shield effect is exhibited inother portions outside the above, and that even with a thickness of350_(″)m of the shield layer, a same shield effect as with a thicknessof 600_(″)m thereof was exhibited except for the edge portion and thecenter portion of the package.

That is, as shown in the internal magnetic field strength distributiondiagram of FIG. 9, in which a position corresponding to a length of 28mm of the magnetic shield layer is specified as a reference to define astandard length thereof, and as shown along the standardized shieldlayer length defined above (refer to the bottom scale in FIG. 9), anintermediate region L1 (which corresponds to the aforementionedintermediate region 41) exclusive of a region L2 which is within 20%inward from both ends of the magnetic shield layer (which corresponds tothe aforementioned edge region 43) and a region L3 which is within 15%outward from the center thereof (which corresponds to the aforementionedcenter region 42) is determined to be a region in which the internalmagnetic field strength is reduced to less than 20 Oe, therebyexhibiting the magnetic shield effect sufficiently. This region L1 whichhas an annular pattern is an area on which MRAM elements 30 can bedisposed.

A package of 160 pin QFP type has approximately a size of 28 mm×28 mm,of which an area available for MRAM is several square mm or 10 square mmat most. In consideration of this and the aforementioned result, MRAMelements 30 are disposed in a part of the intermediate region 41avoiding the edge region 43 and the center region 42 of the magneticshield layer within the package (refer to FIG. 13B). Thereby, even witha thickness of the shield layer set at 350_(″)m, the MRAM was confirmedto have been shielded from the external leakage magnetic field and tohave operated normally.

In the next, using Fe-49Co-2V as the material of the magnetic shieldlayer in the experimental equipment shown in FIG. 5, with the gapbetween the shield layers set at 2 mm, the thickness of the shield layerat 200_(″)m, with an external magnetic field to be applied set constantat 500 Oe, then by changing the length of the shield layers variously,magnetic field strengths in the center portion of the sandwich structurewere measured, the result of which is shown in FIG. 10, anddistributions of the internal magnetic field strengths per length of theshield layer are shown in FIG. 11.

From this result, it is known that the longer the package length (shieldlayer length) becomes, the larger the internal magnetic field strengthbecomes, and that the shorter the package length becomes, the smallerthe internal magnetic field strength is reduced.

FIG. 12 shows a distribution diagram of internal magnetic fieldstrengths relative to the standardized package length, and respectiveregions where the MRAM elements can be mounted or not. Thereby it isrevealed that the internal magnetic field strength distribution occursnot at a constant ratio but occurs depending on a package length.

From FIG. 12, as to the placement of the MRAM elements, it is preferableto dispose them apart from either end portion of the magnetic shieldlayer by 10% or more of the shield layer length inwardly, and in thecase where the magnetic shield layer length exceeds 15 mm, it ispreferable to dispose them apart by 20% or more of the shield layerlength outward from the center of the shield layer.

However, because there may occur a slight change depending on a packagelength, a shield layer material, a gap between shield layers and thelike, irrespective of the aforementioned conditions, it is preferable tocarry out simulation at an initial stage of design to determine optimalpositions of the MRAM elements.

FIG. 13A is a diagram showing respective areas in which the MRAMelements can be installed or can not relative to the magnetic shieldlayer, on the basis of each result in FIGS. 9 and 12.

That is, as shown in FIG. 13A, by avoiding the center region 42 which iswithin 15% outward from the center C of the magnetic shield layer, andthe edge region 43 which is within 10% inward from the edge of themagnetic shield layer, and by disposing MRAM elements 30 in theintermediate region 41 therebetween (which has an annular patternindicated by oblique lines, and which is within 25% of the length of theshield layer), it is ensured for the MRAM elements 30 to be operatednormally.

FIG. 13B shows a hybrid package in a state mounting various otherelements, for example, such as DRAM (Dynamic Random Access Memory) 45,DSP (Digital Signal Processor) 46, RF (Radio Frequency) 47 and the like,together with the MRAM elements 30 on the intermediate region 41 inwhich the MRAM elements are allowed to be disposed. However, as to theaforementioned various other elements, it is not necessarily required todispose them within the aforementioned intermediate region 41. In thecenter region 42, the aforementioned other elements and externalconnection terminals can be disposed as well.

By way of example, as to the soft magnetic material inclusive of theaforementioned exemplary Fe—Co—V systems from which to fabricate themagnetic shield layers, it may be any soft magnetic material at least ifit contains one of Fe, Co and Ni, and may be preferably a soft magneticmaterial which has a high saturation magnetization and/or a highpermeability, for example, such as Fe, FeCo, FeNi, FeSiAl, FeSiB, FeAl,or the like.

As described heretofore, according to the preferred embodiments of thepresent invention, by placing the MRAM elements in the intermediateregion avoiding the edge region 43 and the center region 42 of themagnetic shield layers 33, 34, it is ensured for the MRAM elements 30 tooperate normally without being affected by the internal leakage magneticfield. Moreover, as the intermediate region 41 excepting the centerregion 42 and the edge region 43 is such a region in which the MRAMelements 30 are essentially not affected by the internal leakagemagnetic field even with a thin magnetic shield layer 33, 34, themagnetic shield layers can be designed to have a thinner thickness, as aresult, the MRAM device can be fabricated compacter and morelight-weighted.

Although the invention has been described in its preferred form with acertain degree of particularity, it should be understood that many otherchanges, modifications and combinations are possible without departingfrom the scope of the present invention.

For example, the aforementioned compositions and kinds of the magneticshield layer material, thickness of the layers, arrangements and sizesthereof, or even the structures of the MRAM can be modified variously tothe same effect.

Further, the above-mentioned magnetic shield structures may be combinedappropriately. For example, it is possible to combine the structure ofFIGS. 1A, 1B with the structure of FIG. 2, alternatively to combine thestructure of FIGS. 1A, 1B with the structure of FIG. 3. Still further,it is also possible to omit the lower magnetic shield layer 34 in thestructures described in FIGS. 1A through 4B.

Still more, although the present invention is suitable for applying tothe MRAM, it is also applicable to any other magnetic memory storagehaving magnetic layers capable of magnetization.

As described heretofore, according to the present invention, bydisposing the memory elements in the region excepting the edge portionand the center portion of the magnetic shield layer, that is, bydisposing the memory elements in the intermediate portion between thecenter portion of the magnetic shield layer, where the magneticsaturation easily takes place and the internal leakage magnetic fieldstrength becomes larger, and the edge portion of the magnetic shieldlayer, where no magnetic shield effect exists due to direct exposure tothe external magnetic field, it is ensured for the memory elements tooperate normally without being affected by the internal leakage magneticfield.

1. A magnetic memory device constructed as a magnetic random accessmemory, said magnetic memory device comprising: a memory element havingby laminating a magnetization pinned layer in which the orientation ofmagnetization is pinned and a magnetic layer in which the orientation ofmagnetization is changeable, and a magnetic shield layer formagnetically shielding said memory element, wherein said memory elementis characterized by being disposed avoiding an edge portion and a centerportion of said magnetic shield layer.
 2. A magnetic memory devicecomprising: a memory element having a magnetic layer capable of beingmagnetized, and a magnetic shield layer for magnetically shielding saidmemory element, wherein said memory element is characterized by beingdisposed avoiding an edge portion and a center portion of said magneticshield layer.
 3. A magnetic memory device according to claim 1 or claim2, wherein said memory element is disposed in a region between aposition at 0.1 L inward from one side of said maganetic shield layerand a position at 0.15 L outward from the center of said magnetic shieldlayer toward one side thereof, where a length from one side of saidmagnetic shield layer to an opposed side thereof is L.
 4. A memorydevice according to claim 3, wherein said memory element is disposed ina region between a position at 0.2 L inward from said one side and aposition at 0.15 L outward from the center of said shield layer towardsaid one side thereof, where said magnetic shield layer is provided onboth sides of said memory element, and a distance between said magneticshield layers, a length from said one side of said magnetic shield layerto the opposed side thereof, and an external magnetic field to beapplied are constant respectively.
 5. A memory device according to claim3, wherein said memory element is disposed in a region between aposition at 0.1 L inward from said one side thereof and a position at0.2 L outward from the center of the shield layer toward said one sidethereof, where a distance between said magnetic shield layers, athickness of said magnetic shield layers, and an external magnetic fieldto be applied are constant respectively.
 6. A memory device according toclaim 1 or claim 2, wherein said magnetic shield layer is disposed onthe top and/or bottom of a package having by sealing said memory elementtherein, or/and on the upper portion and/or the lower portion of saidmemory element within said package.
 7. A memory device according toclaim 6, wherein said memory element is present almost allover saidpackage.
 8. A memory device according to claim 1 or claim 2, whereinsaid magnetic shield layer is in the form of a flat film or plate, orhaving concave and/or convex portions thereon, or through-holes such asmesh or slits.
 9. A memory device according to claim 6, wherein saidmagnetic shield layer is formed of soft magnetic material that exhibitssaturation magnetism at 1.8 tesla or more.
 10. A memory device accordingto claim 1, wherein said memory device is constructed such that aninsulating material layer or a conductive material layer is sandwichedbetween said magnetization pinned layer and said magnetic layer, thatwith a magnetic field induced by passing a respective current throughwirings provided on the top and the bottom of said memory element, theorientation of magnetization in said magnetic layer is aligned in aprescribed direction thereby writing information thereto, and that saidwritten information is read out by use of the tunnel magnetoresistanceeffect between said wirings.